1. Field of the Invention
The present invention relates to a separating plate of solid oxide fuel cell stack. More particularly, the present invention relates to a separating plate of solid oxide fuel cell stack having a substrate, a micro channel plate and a sealing guide.
2. Description of the Related Art
In general, a fuel cell is a kind of energy conversion device. Fuel and air are injected to an anode (a fuel electrode) and a cathode (an air electrode) respectively, and ion-conduction via electrolyte is processed with electrochemical reaction. With some condition according to the properties of the electrodes and electrolyte, a fuel cell produces electricity as long as it is supplied with fuel.
Such fuel cell is more effective than conventional generation method, and no pollutant is produced except water when hydrogen is used as fuel. According to the kind of used electrolyte, the operating temperature and characteristic may be diverse, so that various applications are possible in different fields.
In the fuel cell, solid oxide fuel cell (SOFC; Solid Oxide Fuel Cell) is also called as Ceramic Fuel Cell since most of the electrode and electrolyte components of the SOFC comprises ceramic. The solid oxide fuel cell (SOFC), which consists of ceramic as electrodes materials and electrolyte, is operated at high temperature of 600˜1000° C., and could be driven with fuel as hydrogen, carbon monoxide, methane and so on. The SOFC is also developed for residential and distributed power generation systems since cogeneration and combined cycle in conjunction with gas turbine are easily applied. A research in conjunction with coal gas as a large power system is underway.
Since a voltage of one fuel cell is less than 1 volt, a stack should be made by deposing couple of cells in order to achieve the desired output in the solid oxide fuel cell (SOFC). In order to make a stack by laminating flat type solid oxide fuel cell (SOFC), a separating plate is needed for preventing two kinds of gas providing to the fuel electrode and the air electrode from mixing with each other. The separating plate provides an electronic connection between fuel cells as well as a channel for distributing the two kinds of provided gas in the stack.
As material of this separating plate, metal and ceramic material is widely used. The ceramic separating plate is hard to manufacture in a large scale, and has weak mechanical strength and bad mechanical workability for forming the channel. In addition, the ceramic separating plate has low thermal conductivity, so that the heat generated in the reaction of the fuel cell is difficult to disperse. In order to serve as the channel for a reaction gas supply, the ceramic separating plate should be sintered finely. However, a sintering temperature is too high to be sintered at high density.
In order to solve the problem of these ceramic separating plates, the metal separating plate technology is recently and widely developed. However, because the metal separating plate exposes to high temperature and oxidation atmosphere, the insulating oxide scale is formed on the surface of the metal separating plate and interrupts electronic connection between unit cells, so that the performance of fuel cell is greatly decreased. Especially, when the channel is manufactured through the mechanical process on the metal separating plate, a lot of costs and times are consumed as the ceramic separating plate.
Thus, in order to secure the performance of the solid oxide fuel cell stack, the channel should be well formed so that the fuel and air (oxygen) may be uniformly distributed in the entire of the fuel cell located inside the stack.
The separating plate of the fuel cell stack may be counter flow, co-flow, cross-flow and so on according to the position of the manifold and the channel. In the separating plate with the cross-flow channel, supplied gas from the manifold is distributed along a main channel in the horizontal direction and a micro channel in the vertical direction to the direction of the main channel. In the other side of the separating plate, the main channel is formed in the vertical direction so that the two gases flow in vertically crossed direction finally.
In the separating plate, which has a cross-flow type channel in the conventional solid oxide fuel cell stack, gas supplied to the main channel is provided to the micro channel and is used for electrochemical reaction. After the reaction, the gas is combined at the exit ends of the channel and vented to the outside via an outflow manifold. It is not easy to supply gas uniformly to each micro-channel. Once the gas is distributed inside the micro channel from the main channel, re-distribution is not conducted until the discharge.
Additionally, as well as it is difficult to form the micro channel of the separating plate accurately, workability problems were declining because of lots of time-consumption.